Promise a Ship Date

Algorithm

Medium

dates

calendar

shipping

Promise a Ship Date

Sales keeps promising customers "we ship within three working days" — and the warehouse keeps missing it, because three working days is not three calendar days. The Friday order ships Wednesday, not Monday. The subsidiary in Dubai rests Friday and Saturday, not Saturday and Sunday. And no shipment leaves on a public holiday. You are writing the calculator both teams will trust.

Requirements

Create a codeunit named "Working Days Calculator" with two public procedures:

procedure WorkingDaysBetween(FromDate: Date; ToDate: Date; WeekendDays: List of [Integer]; Holidays: List of [Date]): Integer
procedure PromiseShipmentDate(OrderDate: Date; LeadTimeWorkingDays: Integer; WeekendDays: List of [Integer]; Holidays: List of [Date]): Date

A date is a working day exactly when its weekday number is not in WeekendDays and the date itself is not in Holidays. Weekday numbers run 1 (Monday) through 7 (Sunday) — the numbering Date2DWY uses.

What you may rely on — the tests never violate this:

WeekendDays holds between 0 and 6 distinct values, each 1 to 7. It can be empty (a warehouse that never closes) and it never covers the whole week.
Holidays is any list of dates: it may be empty, it may contain the same date more than once, and it may contain dates that fall on a weekend day or outside the range you are looking at.

WorkingDaysBetween returns the number of working days in the range from FromDate to ToDate, both endpoints included:

A holiday inside the range removes its day from the count once — no matter how many times it appears in the list.
A holiday that falls on a weekend day changes nothing: that day was never a working day to begin with.
A holiday outside the range changes nothing.
If ToDate is earlier than FromDate, raise an error with a message that contains the text must not be before.

PromiseShipmentDate returns the date the shipment leaves: the date reached by counting LeadTimeWorkingDays working days strictly after OrderDate:

OrderDate itself never counts, even when it is a working day — the order still has to be picked. A lead time of 1 therefore returns the first working day after OrderDate.
The returned date is always a working day by construction.
If LeadTimeWorkingDays is below 1, raise an error with a message that contains the text at least one working day.

What the tests check

The tests exercise both procedures with fixed dates in July 2026: a full Monday-to-Friday week, a range crossing a Saturday–Sunday weekend, single-day ranges on a working day and on a weekend day, a Friday–Saturday weekend pattern, a holiday inside the range, the same holiday listed twice, a holiday on a Saturday, a holiday outside the range, an empty weekend list, and promises that must step over weekends, a two-day holiday run, and a custom weekend. Both error rules are checked against the exact message fragments quoted above — the lead-time rule with a lead time of zero and with a random negative value. Two tests use a randomized range, weekend pattern of 2 to 5 weekend days, lead time and holidays, and compare against an independent day-by-day count — so hardcoding the fixed examples or handling only two-day weekends will not pass.

Learn More

Hint 1

No built-in date formula knows your parameters: CalcDate's <WD> notation follows the company base calendar, not the WeekendDays and Holidays lists you were handed. Arithmetic shortcuts (whole weeks times five, minus the holiday count) break on custom weekend patterns, duplicate holidays, and holidays that fall on a weekend — think about deciding each calendar day on its own.

Hint 2

One question settles everything: is this single date a working day? It is exactly when its weekday number is not in WeekendDays and the date is not in Holidays — Date2DWY(TheDate, 1) gives the weekday number, and List.Contains answers both membership questions, which also makes duplicate holiday entries harmless. Put that in one local procedure and both public procedures become short loops.

Hint 3

For the count, walk one day at a time from FromDate to ToDate and add 1 whenever the day is working (a Date plus an Integer is a Date). For the promise, start at OrderDate and keep stepping one day forward, counting only working days, until you have counted LeadTimeWorkingDays — the day you stop on is the promise date, and it is a working day by construction.

ALBusiness Central 28.4

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